Hardcover/Casebound: A bound book that has a covering (case) which is made of boards, cloth and/or paper, and usually has foil stamping on it.
Softcover/Paperback: A bound book that has a cover that is made from printed paper, usually with some type of coating or lamination.
Mass Market: A book designed to be sold in large quantities, also known as "rack" size, or more generally known as paperbacks. These are smaller, softcover versions of Trade books.
Digest: Cold web, cross grain paperback up to 5 3/16" x 8 1/4"
Trade: A book or novel that's intended for the general market. Normally either 5 1/2" x 8 1/4", 6" x 9", or 6 1/8" x 9 1/4".

Over forty carton sizes are kept in stock at all times to handle virtually any packing requirements. Packs of 48 copies per carton are most common. The pack specification usually depends on the spine size of the book.